1. Field of the Invention
The present invention relates to a shift control device and a shift control method for an automatic transmission.
2. Description of the Related Art
As well known, a shift control device for an automatic transmission determines an upshift and a downshift of gears according to a gear shift map (gear shift schedule) based on the vehicle speed and the accelerator pedal operation amount (or the throttle opening degree) as described in, for example, Japanese Utility Model Application Publication No. 61-64548 (JP-U-61-64548). FIG. 5 shows an example of a gear shift map based on the vehicle speed and the accelerator pedal operation amount. According to the gear shift determination based on the vehicle speed and the accelerator pedal operation amount (or the throttle opening degree), the gears are shifted based on accelerator pedal operations according to the driver's intention.
In the case where priority is given to satisfying requirement relating to the engine, for example requirements relating to fuel consumption characteristics, exhaust characteristics, and combustion modes, the gear shift determination may be based on the load on the internal combustion engine or the drive force of the vehicle. That is, the fuel consumption characteristics and the exhaust characteristics of the internal combustion engine may be improved by shifting the automatic transmission such that the internal combustion engine operates at an optimal rotational speed and under a desirable load in terms of fuel consumption, emission, and so forth. However, gear shift determination based only on the load of the internal combustion engine and the drive force does not allow the gear shift operation of the automatic transmission to reflect the driver's intention based on accelerator pedal operations.